1. Field
Embodiments of the disclosure relate to electronic devices, and more particularly, in one or more embodiments, to wide common mode difference amplifiers.
2. Description of the Related Technology
A difference amplifier is a special purpose amplifier designed to measure differential signals. One feature of a difference amplifier is its ability to remove unwanted common mode signals. Unlike most types of amplifiers, a difference amplifier is typically need to measure voltages beyond the supply rails, and is used in applications where large dc or ac common-mode voltages are present. It is ideal for current and voltage monitoring. For example, it can be used to amplify the voltage drop across a current shunt resistor, which is placed in series between power bus and some form of load. The amplifier performs current measurements across a shunt resistor in a variety of applications, such as, but not limited to digital audio, medical, automotive, telecommunications, or power management. To reduce power dissipation of the shunt resistor, it is desirable to keep the amount of resistance small. Therefore, the voltage drop across the resistor is usually small, for instance, hundreds of millivolts (mV) or less. However, the input common mode voltage can vary widely depending on applications. For example, to measure a load current for high-power class D amplifiers, the common mode voltage can be a sine wave with a peak-to-peak voltage of 300V, and frequency up to 20 kHz; in an ultrasound imaging system, the input common mode voltage can be about −120V; in telecommunication systems, the input common-mode can be −48V or +48V; and in automotive applications, the input common mode can be a pulse-width modulated signal varying between −2V to 65V at frequencies up to 20 kHz and duty cycles varying from 2% to 98%. Therefore, there is a need for a universal difference amplifier to handle such a wide common mode input range in order for operations in a variety of applications.
A conventional solution for AC current sensing uses resistor dividers in an input stage of a difference amplifier that is powered by a dedicated dual power supply. The resistor divider is configured such that it attenuates the input common mode voltage into an input range that can be handled by an input amplifier, such as the dual power supply range. However, there are several drawbacks with this approach. For instance, a dual power supply is required. The resistor divider increases the input referred noise, offset, and offset drift, and reduces the bandwidth of an amplifier.